With cycles, how do I render only highlights and only shadows and nothing else?
I'm not exactly sure about what features you need to highlight, and you might not like my solution because it will just tell "global" highlights from "global" shadows, instead of underlining "local" sharp changes in lighting (however, I think this is exactly what your example image is doing).

With that in mind, I think you can start with a very simple Compositing Nodes setup:

Take your RenderLayer input, and between it and the output, add a "RGB to BW" and a "ColorRamp" node.

Move the sliders around on the ColorRamp node to find your highlight/shadow range.